ublk: move zone report data out of request pdu

ublk zoned takes 16 bytes in each request pdu just for handling REPORT_ZONE operation, this way does waste memory since request pdu is allocated statically.

Store the transient zone report data into one global xarray, and remove it after the report zone request is completed. This way is reasonable since report zone is run in slow code path.

Cc Damien Le Moal <[email protected]>

Cc Andreas Hindborg <[email protected]>

Signed-off-by Ming Lei <[email protected]>

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